Labelling is an especially serious concern in the fabrication of small or miniature electronic components involving semiconductor integrated circuit (IC) processing in which the semiconductor devices start with a wafer into which the individual devices are formed. After formation, the wafers are scribed or cut into dies, with each die having one integrated circuit therein. Each wafer and each die therein is tested by probing. From the beginning of automated wafer probing, the technique for differentiating Good Dies from Not Good Dies on a wafer containing many dies has remained essentially unchanged. At the probing machine, each die is provided with an ink dot indicating a fail, and each rejected die is discarded. The ink dots' average size depend on the type of dot dispenser used, but range in the main between 0.005" and 0.021" in diameter. With the increase in die dimensions and complexity and cost, design redundancy has been instituted such that a failed section of a die or IC does not impair its further marketability whether as the originally intended device or as a new device. To this end, rather than just indicating a pass/fail, it is important to label the die with information concerning potential use for the die. If the partially failed device is not rejected, it can be identified as such.
While a pass/fail labelling system differentiates between dies as either Good or Not Good, for differentiating among dies on a more complex basis such as quality and/or test results, the only method existing heretofore for recording quality-of-die information from the probing is by wafer mapping in which the x, y position of each die on a wafer is recorded, as well asinformation about the die during the probing process. Probing is performed with the probe tips preferentially connected to a test computer very nearby, such that each die on the wafer becomes known in address or x, y location on the wafer, quality and relevant other parameters, and preferentially storing this information on appropriate ambulatory computer readable memory. This information in the ambulatory memory storage travels with the wafer in the subsequent processing steps, and is used to separate the types of dies once the wafer has been diced and the individual dies are sawed apart for handling in separate groups. The mapping is also used for recording device history. This wafer mapping technique is to this day not universally accepted, and causes problems with the easy flow of material on the manufacturing line, since it requires that each wafer, then each die or die group, be accompanied throughout its processes by a computerized data bank identifying its quality and other parameters. Not all existing processes and machinery are amenable to this technique, and considering the large quantity of ICs manufactured today, the management burden is too gargantuan to be practical except for unique cases.
In present day practice, qualitative information gathering is performed at the probing station, and differentiation is done after sawing the devices apart from the original wafer form by physically transferring each device according to quality type, generally to a carrier called `waffle pack`, which is a container holding a number of devices, each device in a separate cavity in a waffle-like container. However, lacking wafer mapping the differentiation between groups of often times based soley on the Good/Not Good ink dot marking. The devices stored in the waffle-like container are very likely to become misoriented in the cavities, and very often even turn upside down, due to the handling. With each waffle pack goes a label of some fashion identifying the devices' type. Another method transfers each device onto a sticky tape, usually in the form of a ribbon with cavities, each tape receiving one type of device. Another method applies each device onto a ribbon whose links ultimately become part of the final device form, if for tape automated bonding, Chip-On-Board techniques, encapsulation, or for hybrids.
It is obvious that much of the yield loss in the manufacture of integrated circuits is due to the arbitrary writeoff of marginal devices indeed suitable for some purpose, but where the process of identifying them as such throughout the manufacturing process would require excessive attention to relatively small number of devices per wafer. However, in the cumulative, this number becomes very large indeed.
Another source of excessive yield loss takes place in the handling of the waffle packs, due to mishandling or other mishaps, including mislabelling. Another source of costly effort is in the attempt to orient the devices in the various assembly processes, including turning over and directional orientation, purely on the basis of the visible pattern on top of the device created by the etching/metallization IC generation steps. This need for orientation has bred a whole new industry, that of pattern recognition, involving expensive systems including solid state sensors, cameras, computers and software. A restriction on the use of custom technology for limited quantities is also generated by the practical difficulties of creating more than one device type on a particular wafer, and from the difficulties in tracing individual or small groups of devices in the manufacturing stream. Inevitably, the yield losses and restrictions on manufacturing flexibility translate into higher costs and lost opportunities.
Microlabels, other than ink dots, have not heretofore been used to label dies or any other objects, small or large. In fact microlabels have not heretofore been produced for any purpose. Labelling has existed for large objects which has involved bar code labelling either black/white or color.
With respect to color coded labels, U.S. Pat. No. 4,053,433 describes labels made of colored layers, broken randomly into uneven and geometrically undefined pieces or chips. These chips are produced in a batch process in which all chips broken from a sheet have the same bar code. To use the chips, they must be separated, classified as to bar code and then affixed to the article to be labelled. Thus changing the code for each article is not feasible on-the-fly.
Moreover, the chips have ragged edges. This prevents reading of the code because the code is carried at the edge of the chips in terms of its colored layers. To overcome the reading problem, several techniques are used. One is the use of many such pieces, randomly sprinkled onto the product, and bonded in place. In the process of bonding, some of the pieces adhere with the edges facing the viewer, enabling reading. Another technique involves the creation of at least one magnetic layer. Thus under the influence of a magnet, the chips move after deposition, to erect themselves such that the edges now face the viewer. This however creates a very rough, if colorful, surface on the product. Another possibility is that to inspect the colors, one must physically remove at least one chip, and then use a magnet to hold it in place under an optical instrument. Other manufacturing techniques enable the creation of very large chips where the chip is bondable to the tagged product, with the plane of the layers visible to the viewer without the difficulties inherent in the chips described above. However, this method does not lend itself easily to miniaturization.
Other related bar code labelling patents include U.S. Pat. Nos. 4,329,393; 3,861,886; 3,772,200; 4,390,452; 4,044,227; 3,858,506; and 4,844,509.
Moreover, Swedish patent 051613-01 issued Feb. 18, 1988 describes a batch process for normal size color coded labels where the color layers are clearly visible to the viewer at all times. The difficulty this label has in common with all earlier labels is that it must be prepared and stored prior to application, thus requiring batch processing and extensive planning, materials handling, and materials management.
Moreover, existing marking systems tend to disturb the surface of the marked objects so that the marked surface feels rough after the marking. Additionally, it is often preferable to decode markings automatically. This is the case in automated ID card control machines and automated mass production control stations. As will be appreciated in this application if a very small overall size label is desired, marking makes it necessary to locate the label and the decoder with exact precision relative to one another, which can be a problem.
Further, with respect to very small bar code labels, the separation of the colors of the bars on the labels and marking ribbons is difficult mainly because of the very small size of the color bars.